The Collaborative International Dictionary of English v.0.48:

Ally \Al*ly"\, v. t. [imp. & p. p. Allied; p. pr. & vb. n.
   Allying.] [OE. alien, OF. alier, F. alier, fr. L. alligare
   to bind to; ad + ligare to bind. Cf. Alligate, Alloy,
   Allay, Ligament.]
   1. To unite, or form a connection between, as between
      families by marriage, or between princes and states by
      treaty, league, or confederacy; -- often followed by to or
      with.
      [1913 Webster]

            O chief! in blood, and now in arms allied. --Pope.
      [1913 Webster]

   2. To connect or form a relation between by similitude,
      resemblance, friendship, or love.
      [1913 Webster]

            These three did love each other dearly well,
            And with so firm affection were allied. --Spenser.
      [1913 Webster]

            The virtue nearest to our vice allied. --Pope.
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   Note: Ally is generally used in the passive form or
         reflexively.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Allied \Al*lied"\, a.
   United; joined; leagued; akin; related. See Ally.
   [1913 Webster]

WordNet (r) 3.0 (2006):

allied
    adj 1: related by common characteristics or ancestry; "allied
           species"; "allied studies"
    2: of or relating to or denoting the Allies in World War II; "an
       Allied victory"; "the Allied armies"
    3: of or relating to or denoting the Allies in World War I; "an
       allied offensive"; "the Allied powers"
    4: united in a confederacy or league [syn: allied,
       confederate, confederative]
    5: joined by treaty or agreement

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "allied":
   affiliate, affiliated, affinitive, agnate, akin, assembled,
   associate, associated, avuncular, banded together, bound,
   bracketed, cabalistic, closely related, cognate, collateral,
   collected, confederate, confederated, congeneric, congenerous,
   congenial, conjoined, conjugate, connate, connatural, connected,
   consanguine, consanguinean, consanguineous, conspecific,
   conspiratorial, copulate, corporate, correlated, correlative,
   coupled, distantly related, enate, enleagued, federate, federated,
   foster, gathered, german, germane, hand-in-glove, hand-in-hand,
   implicated, in cahoots, in league, in partnership, in with,
   incident, incorporated, integrated, interlinked, interlocked,
   interrelated, intimate, involved, joined, kindred, knotted,
   leagued, linked, married, matched, mated, matrilateral,
   matrilineal, matroclinous, merged, novercal, of that ilk,
   of that kind, of the blood, paired, parallel, partners with,
   patrilateral, patrilineal, patroclinous, related, sib, sibling,
   similar, spliced, teamed, tied, twinned, undivided, united,
   unseparated, uterine, wed, wedded, yoked